Luminescent tube



Sept. 5, 1939. R B LEONARD ET AL 2,171,705

LUMINESCENT TUBE Filed Feb. 7, 1938 3 v w owto ai RaseZZZZeomrd FVZZZZQ IZEZea/Mrd Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE LUMINESCENT TUBE Application February 7, 1938, Serial No. 189,066

3 Claims.

This invention relates to illuminating tubes of the luminescent type utilizing air-evacuated chambers containing an inert gas or gases, such is determined by the effectiveness and stability of the gases with which they are charged. It has been noted that after the tube has been used for a certain period of time which, of course, is quite variable with difierent tubes, the charging gas apparently becomes absorbed or dissipated so that the tube no longer functions in its normal manner. This requires that the defective tube shall be removed from the sign of which it forms a part and taken to a factory and supplied with a fresh quantity of gas before it can be again restored in its operative position in the sign frame. This operation of repairing or replacing a defective neon tube is comparatively slow and quite expensive and, of course, while it is taking place, the sign is out of service.

It is, therefore, an outstanding object of the present invention to provide a luminescent neon tube which, when the original charge of gas supplied thereto becomes exhausted or deficient in quantity to a point where the operation of the tube is threatened, provides a means by which an additional quantity of the charging gas will be automatically supplied to the tube in order to replenish the original charge and, without interruption in operation, to greatly prolong the normal eifective life of a tube of this nature.

Another object of the invention resides in the provision of a neon tube formed with a sealed chamber adapted for the reception of a reserve supply of neon, or other charging gas, the said chamber being provided with a fusible wall disposed adjacent to one of the electrodes of the tube, so that when the original charge of gas within the tube becomes diminished, the added heat released from the electrode by such gas deficiency will first melt or soften the fusible wall of the chamber to such an extent as to permit the reserve charge of gas within said chamber to enter the interior of the tube and restore the gas charge to a volume permitting of normal and continued operation of the tube.

Further objects and advantages will apparent as the description proceeds.

In the accompanying drawing:

Figure 1 is a perspective view of a neon tube;

Fig. 2 is a side elevation thereof disclosing the ends of the tube equipped with the reserve gas chambers formed and arranged in accordance with the present invention;

Fig. 3 is an enlarged longitudinal sectional view taken through one end of the tube disclosing the formation of the gas chamber and its relation to an associated electrode;

Fig. 4. is a vertical transverse sectional view taken through the tube on the line IVIV of Fig. 3;

Fig. 5 is a detail view in side elevation illustrating the manner of evacuating the chamber and the interior of the tube;

Fig. 6 is a detail vertical sectional view through a slightly modified form of tube having the features of the present invention.

Referring more particularly to the drawing, the numeral I designates a neon tube of the type now widely used in the construction of advertising signs. Such tubes, as their name implies, comprise tubular casings, usually made of glass, and wherein the interior of the tube is formed to present a sealed chamber under a high degree of vacuum and containing raw inert gases of the monatomic group, including neon, helium, argon.

In the present invention, we do not limit ourselves to any one or moreof these gases, since any gas or combination thereof now generally used in connection with the manufacture of tubes of type may be employed. It will be understood, therefore, that when the term neon is used in the present specification and claims, it is employed in a generic sense to include all gases now used commercially in luminescent tubes of the type under consideration.

The tube 9 may be blown or otherwise formed into any desired physical form, depending upon the specific uses to which it is to be placed, as will be readily understood by those skilled in the art. The ends of the tube l are provided with the customary electrodes 2 to which the usual high voltage but low amperage alternating electric current charges are applied. The tube so far described is of standard construction and operation and it is to the improvement therefore that the present invention is directed.

As previously stated, after a tube of this type has been in use for some time, the original charge of neon becomes absorbed or dissipated by reason of the sustained operation of the tube, and to become restore the tube to its original effectiveness, the supply of the charging gas must be replenished. This is usually done by demounting the tube from its operating position in a sign, an operation requiring considerable time, loss of use of the sign and certain expense.

It is the aim of the present invention to provide a tube wherein the gas supply is automatically restored when the gas originally supplied to the tube dissipates to a predetermined degree. One way of accomplishing this result is to form the end of the tube with a capsule 3, the glass wall of which is somewhat thinner or weaker than the glass wall of the tube I. This capsule is adapted to contain under approximately atmospheric pressure a suitable quantity of neon, or other charging gas, which in quantity or by weight is sufficient to charge the entire internal area of the tube l to provide for normal operation of the latter. It will be observed that one end of the capsule 3 is arranged adjacent to but spaced from an adjoining end of one of the electrodes 2.

During normal operation of the tube, the surface area of the electrode and the quantity of the charging gas in the tube are so proportioned that any heat developed in the tube by its operation does not have any appreciable weakening effect on either the walls of the tube or of the ca sule. However, as the original charge of gas to the tube reaches a state of exhaustion, the internal heat of the tube increases due to the increased electrical resistance set up by the diminution of the gas supply. In an ordinary neon tube, when the same fails, it is a matter of common observation that there is a small opening in the glass wall of the tube adjacent to one or the other of the electrodes, this opening being produced by the excess heat. We, therefore, form the capsule 3 to include a glass wall somewhat thinner than the tube I, or, at least, to provide the capsule with a locally weakened portion. The strength of the glass wall of the capsule, or its locally weakened area, is predetermined so that when the gas supply fails and the temperature of the tube increases, one end of the capsule, by being disposed in the electric field of the electrode, becomes heated to the fusion point more rapidly than the glass wall of the tube 1. This enables the reserve supply of gas contained within the capsule to flow into the vacuumized interior of the tube I, restoring the normal operation of the tube and prolonging its life by reason of the added charge of gas automatically supplied.

We preferably locate one of the capsules 3 adjacent to each of the electrodes of the'tube, so

that by this construction, the normal life of a.

neon tube is increased and, moreover, no care or skilled attention need be given the tube during this augmented period of usefulness.

In the manufacture of the tube, that portion thereof containing the capsules 3 and designated at A in the drawing, is manufactured separately from the end sections B in which the electrodes are contained, the sections A and B and the body section C of the tube being united by fusion along the planes indicated at D and E, prior to the exhaustion of air from the tube and the charging of the same with gas. The capsule 3 is supported in an axial position within the section A of the tube by means of a ported web 4 which joins; with an external ported projection 5, the latter being arranged contiguous to a corresponding projection 6 formed with the body section of the tube. Following the joinder of the sections A, B and 0 of the tube, the ports of the projections 5 and 6 are open to the atmosphere and may be joined with a suitable type of vacuum pump (not shown) in order that the interior of the tube and the capsule may be evacuated of air and reduced to a desired degree of vacuum, which may be noted by means of the gage I. The regaired amount of neon or other charging gas is then introduced into the interior of the tube through the projection 6, and a corresponding amount of gas is introduced into the internal chamber 8 of the capsule 3. The projections 5 and 8 are then fused to close their ports and to hermetically seal the interior of the tube and the capsule or capsules 3.

Due to the reduced space or volume of the chamber 8 of the capsule as compared with the interior of the tube, the gas or gases supplied to the chamber 8, and held therein in reserve, will be substantially greater in pressure than those contained in the interior of the tube, since a high degree of vacuum must be maintained within said tube to provide for its desired operation. Usually the gases held in reserve in the capsule 8 are at about atmospheric pressure.

In view of the foregoing, it will be seen that the present invention provides a neon tube with a simple and automatically operating means by which the proper amount of charging gas may be maintained within the tube to insure its successful operation over greatly extended periods of time than can be obtained with a neon tube of conventional design. As stated, the invention may be embodied in many different physical forms without departing from its fundamental principles of design and operation.

For instance, as disclosed in Fig. 6, the section A of the tube includes a tubular jacket 9 which provides an annular reserve gas supply chamber In disposed in the immediate proximity of an adjoining electrode 2. Various other constructions capable of carrying out the same results, objects and advantages, will be apparent to those skilled in the art and it is our desire to include within the scope of our invention all such constructions that may be said to fall fairly within the purview of the following claims.

, What is claimed is:

1. A luminescent tube comprising a vacuum chamber containing neon under reduced pressures, electrodes entering the ends of said chambar, and a glass capsule disposed axially within said tube adjacent to one of said electrodes, said capsule being structurally weaker than the walls of said tube and containing a reserve supply of the inert charging gas normally maintained within said tube, said capsule responding to abnormal heat developed within said tube by depletion of the original gas supply to effect the flow of the reserve gas normally sealed therein into said tube, whereby to restore the gas balance of the tube.

2. A luminescent tube formed with a main chamber for the reception of a charging as under sub-atmospheric pressure, spaced electrodes entering said chamber, and a normally closed receptacle disposed axially within said tube adjacent to one of said electrodes, the portion of said receptacle arranged nearest to said electrode being structurally weaker than the walls of said tube,'said receptacle containing a reserve supply of the charging gas normally maintained within heat developed within said tube by depletion of the original gas supply of said chamber to elect the release of the reserve supply of gas originally sealed within said receptacle and its delivery to said main chamber, whereby to restore the normal gas balance of the chamber.

3. A luminescent tube comprising a glass body formed with a main chamber adapted for the reception of a charging gas maintained under sub-atmospheric pressure, spaced electrodes entering said chamber, and a normally closed receptacle of smaller volumetric capacity than said main chamber, said receptacle having sealed therein a reserve supply of said charging gas 

